Several stress proteins have been reported in Neisseria including proteins induced with heat chock and ones induced under iron deficient growth. We have characterized a 65-kDa stress protein enhanced under growth in stationary conditions and found that iron concentration of the medium had no influence on the enhancement of this protein. We have purified this protein using a combination of column chromatography and sucrose density gradients. Electron microscopy of the purified protein revealed structures very similar to the GroEL protein of Escherichia coli. The N-terminal amino acid sequence analysis reveals about 58% identity with the E. coli protein. We have also purified and characterized another 55-kDa protein which partitions in the same fraction as the meningococcal stress protein. This protein was found to be Glutamine synthetase by enzymatic activity and electron microscopy. Its structure was found to be identical to the E. coli glutamine synthetase and it cross reacted with the polyclonal antibody to E. coli glutamine synthetase. We are studying the immunogenicity of the 65-kDa stress protein and its role in the assembly of glutamine synthetase.